Mitt Romney faces the most important week of his political life. Wednesday night's first television debate in Denver could be his last chance to rescue his presidential campaign.

Since the Republican Party convention Mr Romney has suffered a gradual but steady decline in the polls.

His secretly-recorded comments to donors last month that he did not worry about 47 per cent of the electorate has done enormous damage.

The race is still close nationally but in the all-important swing states he is losing ground to his Democrat opponent, Barack Obama.

As ever, most states are pretty much guaranteed to land in the Republican or Democrat camp. But a few in the middle are still all to play for and both campaigns have been spending most of the time in this handful of states.

The way the maths is currently landing, to have any chance of winning Mr Romney must now start building a lead in almost all of the nine swing states that will determine the election on November 6.

The best chance he has of doing so is through a spectacular success in this month's three upcoming television debates against Mr Obama.

Both men have been intensively coached by their teams. Mr Obama has been at a desert resort in Nevada and Mr Romney has been with his key advisers in Massachusetts before heading to Denver in Colorado.

Debates have changed contests in the past. Most famously in 1980.

Ronald Reagan turned the tables on Jimmy Carter in 1980

Democrat Jimmy Carter was leading Republican Ronald Reagan by around 10 per cent in the polls but left the event badly wounded.

"There you go again," quipped Mr Reagan at one point, curtly parrying a potentially-dangerous blow by Mr Carter and giving US politics one of its most memorable quotes.

But it was the question: "Are you better off than you were four years ago?" that most people credit Mr Reagan with for turning around the contest.

Observers have pointed out that the polls had already been moving heavily in Mr Reagan’s favour before the debate, but there is no doubt it made a difference.

Mr Romney has been watching the polls moving against him. He is also up against a different contender.

Mr Obama can be professorial, haughty and aloof. He can appear arrogant, and long-winded. But he remains a daunting opponent for a man who seems unable to keep his foot out of his mouth for long.

Mr Obama has the most to lose and therefore is expected to play things defensively.

Mr Romney has no choice but to go on the offensive. In the race for the Republican nomination he did so effectively in two debates in Florida against Newt Gingrich.

He will be hoping for the same success on Wednesday night, knowing this could be make or break time for his campaign.